This invention relates to a dehydrator including a dehydration tub rotated at a high speed by a motor for dehydrating clothes contained therein.
In fully automatic washing machines, for example, a rotatable tub serving both as a wash tub and a dehydration tub is rotated for dehydrating clothes to be washed. An induction motor has been generally employed for driving the rotatable tub in the conventional fully automatic washing machines. The rotational speed of the induction motor cannot be freely varied and accordingly, is substantially invariable. Consequently, the rotational speed is rapidly increased to a value determined depending upon the number of poles when the induction motor is energized.
Upon start of the dehydrating operation, the rotational speed of the rotatable tub is rapidly increased, reaching its maximum value. The maximum rotational speed of the rotatable tub is usually set at 850 r.p.m. which value is also a rated rotational speed. Since this rotational speed is low for the dehydrating operation, a dehydrating period of time is increased in compensation for the low rated speed so that the dehydration efficiency is increased.
Upon start of the dehydrating operation, a large amount of water contained in clothes is shaken off and discharged out of the rotatable tub. Since the rotational speed of the rotatable tub is rapidly increased to the maximum speed in the prior art, a large amount of water is discharged from the rotatable tub and a force of the discharged water is suddenly intensified particularly at an initial stage of the dehydrating operation. Consequently, the discharged water collides with a great force with the inner peripheral wall of a water-receiving tub in which the rotatable tub is enclosed, producing a loud noise.
On the other hand, the dehydration efficiency is not increased above a certain value at the maximum rotational speed in the prior art even when the dehydrating period of time is increased. To solve this problem, it is proposed that the rotational speed of the rotatable tub be increased above the rated rotational speed. In this case, however, the rotational speed of the rotatable tub agrees with a resonant point of the outer cabinet of the washing machine, resulting in a loud vibrational noise produced from the outer cabinet. Alternatively, the rotational speed of the rotatable tub passes the resonant point of the outer cabinet in the process that it is increased, also resulting in a loud vibrational noise produced from the outer cabinet.